ES2226115T3 - GRAPHIC MATERIALS WITH MICRODOMINIUMS AND PROCEDURE FOR THEIR PRODUCTION. - Google Patents

Abstract

Method for the production of graphite materials with microdomains by decomposing a hydrocarbon fuel in a plasma reactor consisting of a decomposition chamber connected to a plasma generator, in which the plasma reactor is fed with H2 as a gas plasma former, characterized in that the hydrocarbon fuel decomposes in a two-step process in which the hydrocarbons are subject to a first decomposition step in which the hydrocarbon fuel is introduced into the decomposition chamber in the vicinity of the zone of the plasma arc and mixes with the plasma gas, and in which the process parameters are adjusted in such a way that the hydrocarbons do not reach the pyrolysis temperature and only partially decompose to form polycyclic aromatic hydrocarbons (PAH) , and in which the hydrocarbons in the form of PAH, after the first step of composition, are mixed with the gas of the pl asthma and are reintroduced as part of the plasma gas in the area of the plasma arc in the decomposition chamber and undergo a second decomposition step, in which the process parameters are adjusted such that in the arc zone from plasma, PAHs are completely converted into graphite materials with microdomains.

Description

Graphite materials with microdomains and Procedure for its production.

Field of the Invention

The present invention relates to a method for produce graphite materials with microdomains for use in plasma processes, and to produce new graphite materials microconical For graphite materials with microdomains it is done reference to fullerenes, carbon nanotubes, structures of open conical carbon (also called microcones), preferably flat graphite sheets, or a mixture of two of The mentioned structures. The new carbon material consists in open carbon microconos with total disclinations 60º and / or 120º, which correspond to cone angles of 112.90 and / or 83.6º respectively.

Background of the invention

There is currently a great interest in new Carbon materials for their exclusive and innovative properties. For example, carbon materials can be useful for achieve high hydrogen energy storage, to its use in purification processes as well as for different applications within the electronic and pharmaceutical sector. The properties are sensitive to the microstructure of the material of carbon, which may vary according to the degree of graffiti and the introduction of non-hexagonal rings in the network. Fullerenes they constitute examples of new graphite structures, in the which the introduction of 12 pentagons in the hexagonal network gives rise to to closed frames [1]. Carbon nanotubes too they constitute an example of such possibilities [2]. The structures open conics are another example of the structures of possible graphite, but only three of the five have been synthesized possible classes [3, 4, 5].

The recent interest shown by fullerenes and nanotubes is related, among others, to its use in the field of hydrogen storage. Consequently, it has been described for nanotubes a hydrogen storage that reaches a amazing 75% by weight [6]. If so, it will probably represent a great breakthrough in a practical hydrogen storage system for use in the transport sector. It has been proposed that Cellular cars of the future that use this technology storage can reach an autonomy around 8,000 km.

In the case of fullerenes, it is achieved recover more than 7% by weight of the hydrogen added reversibly [7, 8, 9]. Fullerenes have also been used as a mixture of solid phase with intermetallic compounds or metals to achieve high hydrogen contents, that is, 24-26 H atoms per fullerene molecule [10].

The flat graphite material formed by stacking of two-dimensional sheets has a surface Great for absorbing the elements and compounds housed. Do not However, in this type of materials the absorption process is limited by diffusion and the greater the graphite domain, The slower the absorption. It might be interesting to have high graphite materials in which domains were so small that the material housed could easily reach all graphite microdomains by percolation through carbon raw material. The Accessibility of microdomains could be further improved if some  or all the domains will present a disclination, having preferably each domain a discretion less than or equal to 300º to provide cavities, or micropores, to allow flow of the material housed.

A frequent problem that exists with the methods Current synthesis of these graphite materials is the low production yield Fullerenes are usually synthesized vaporizing graphite electrodes by arc discharges of carbon with a reduced atmosphere of inert gas. One has been described  conversion speed in fullerenes of 10% -15%, corresponding at a generation speed of almost 10 grams per hour [11].

The carbon arc method is also the one that It is most often used for the production of nanotubes of carbon. Under optimal conditions, yields of the nanotubes of approximately 60% of the core material [2]. Even so, the yield obtained reaches quantities in grams

Small unspecified quantities are obtained of open conical carbon structures heating with a resistance a carbon sheet and then condensing the carbon vapor on a pyrolytic graphite surface with high orientation [3, 4]. Cone angles produced with this method they reached approximately 19º [3], and 19º and also 60º [4]. He heating of the carbon rod with a resistor and the subsequent deposit on colder surfaces was used to produce cones with apparent cone angles of approximately 39 ° [5]. It can be demonstrated from a continuous sheet of graphite that only five types of cones can be assembled, in which each domain is defined exclusively by its topological discernment  TD that is given by the general formula:

TD = N x 60 degrees, in which N = 0, 1, 2, 3, 4 or 5,

The structure of these graphite domains is can describe in general terms as sheet stacks Graphite with flat structures (N = 0) or conical (N = 1 to 5). Therefore, to date, two of these structures that have cone angles of 83.6º and 112.90.

Summary of the invention

An objective of the present invention is providing a new method as defined in claim 1 to produce graphite materials with microdomains. The method can provide important performance rates even above 90%.

Another objective of this invention is to provide the method defined in claim 1 which is suitable for Industrial scale production of graphite materials with microdomains

In addition, it is an object of this invention to provide a method that can produce graphite materials with microdomains that consist at least in part in a new highly crystalline graphite material composed of open conical carbon structures that prefer cone angles of 83.6 ° and 112 , 9th, which corresponds to
N = 1 and 2. The rest of the materials with graphite microcones are fullerenes, carbon nanotubes, the other open carbon cones (N = 3, 4, or 5), preferably flat graphite sheets (N = 0), or a mixture of two or more of them.

Brief description of the figures

A representation is shown in Figure 1 Schematic of the reactor and the surrounding equipment.

Figure 2 shows a photograph of the samples obtained with the transmission electron microscope, in which reveal the different types of microconic carbons open carbons of the invention.

The expected angles are shown in Figure 3 in the perfect graphite cones, that is, 19.2º, 38.9º, 60º, 83.6º and 112.9º, which represent a total discrimination of 300º, 240º, 180º, 120º and 60º, respectively. In addition, a graphite sheet that has an expected angle of 180º and a total discrimination of 0º.

Figures 4A, 4B, 4C, 4D and 4E show a example of domains of each type of discrimination 60º, 120º, 180º, 240º and 300º, respectively, present in the invention.

Detailed description of the invention

The invention is based on the decomposition of carbon hydrocarbons and hydrogen in a process developed in plasma. The plasma arc is formed in a plasma generator that consists of tubular electrodes in which the internal electrode receives a direct voltage electric current with a polarity and in which the external electrode is connected to the polarity opposite from the power supply. Generator plasma is installed next to a decomposition reactor in which the reactor has been designed as an insulated heat chamber defined with An outlet for the final products. Plasma gas is recycled in the process. A more detailed description of the general process and equipment in Norwegian patent application no. 176522

The structure of the resulting carbon material It will depend on the following three process parameters: speed of introduction of hydrocarbons, enthalpy of gas of plasma and time of stay. By varying these parameters, the resulting carbon material will be in the form of black carbon conventional, in the form of graphite materials with microdomains or in the form of a mixture of both. In this invention we will describe process parameters to optimize graphite materials With microdomains.

The hydrocarbons are introduced into the reactor of decomposition around the plasma arc zone using an injector of its own invention that aligns with the sprayer of hydrocarbon in the axial direction of the reactor, and that has designed so that thick drops form. It is made of this way to delay the evaporation of the hydrocarbon and, of this mode, the formation of graphite material is optimized with microdomains as explained below more detailed.

The energy is supplied from the plasma arc to heat the plasma gas. Part of the energy coming from arc will be used to heat the reactor walls, as well as the own plasma generator. The resulting energy content of the plasma gas (the enthalpy of plasma gas) is sufficient to evaporate the hydrocarbons. The hydrocarbons begin to cracking and polymerization occurs, which results in the formation of polycyclic aromatic hydrocarbons (PAH). PAHs they are the base of the graphite sheets that form the microdomains. The enthalpy of plasma gas is maintained at a level such that the main fraction of gaseous hydrocarbons does not reach pyrolysis temperatures with the rate of introduction specified and the residence time used. However, it will be inevitable that a small fraction of the power reserve reach enough energy during the residence time in the reactor to reach the pyrolysis temperature and convert, consequently, in conventional black carbon. This fraction must Stay as low as possible.

PAHs leave the reactor with plasma gas and is introduced once more into the reactor as part of the gas of plasma. Plasma gas enters the energy intensive zone of the plasma arc, where PAHs become a fraction second in graphite microdomains.

The speed of introduction of the reservation of feed to optimize graphite materials with Microdomains is of the order of 50-150 kg / h in a reactor used by the inventor, but not limited to this interval. Reserve feed rates could be used Feeding both higher and lower. The performance of Graphite microdomain material is greater than 90% in optimal conditions. At least 10% of those domains have total disclinations greater than 60º. Considering the speed of introduction of the power reserve used, industrial quantities of carbon material are achieved with microdomains By increasing to scale, you will get a price that this at the same level as commercial black carbon per unit of material weight

A representation is shown in Figure 1 reactor schematic In Norwegian patent application no. 176511 includes more details about the reactor and the equipment that surrounds.

A typical example of the content of the material with microdomains. Each piece of the sample it forms simple graphite domains and the alignment of the sheets of each domain is typically turbostatic, as determined with the electron microscope. The diameter of the domains is usually less than 5 microns and the thickness is less than 100 nanometers

If the cone is made with a foil uninterrupted graphite, except at its open end, they are only five types of cones possible, due to the symmetry of graphite. These types correspond to a total discrimination of 60º, 120º, 180º, 240º and 300º. A total discrimination of 0º corresponds to A flat domain. In Figure 3, the schematics are shown planned angles for these structures. In Figures 4A, 4B, 4C, 4D and 4E show examples of each of these types of domains It is important to note that all cones are closed in the vertex Conical domains represent at least 10% of the material. The material of this invention consists of microdomains of graphite of well-defined TD total disclinations (curvature), which has discrete values that are given by the formula

TD = N x 60 degrees, in which N = 0, 1, 2, 3, 4 or 5,

and corresponds to the effective number of pentagons necessary to produce a total discrimination in particular.

The results on which the process is based indicate that total disclination is almost always determined in the nucleation stage Previously, it has been determined that the probability of forming pentagons on the nucleus depends on the temperature [12]. Consequently, by varying the parameters of the process, including, among others, the increase in the temperature of the reaction, you can increase the number of pentagons on the core, leading to the formation of nanotubes or frames closed.

The small size of the domains and the presence of several disclinations in the graphite material produced in the The present invention are useful for the incorporation of elements and compounds housed. The space that remains between domains will provide micropores for material flow housed, so that it can reach each domain. The small Domain size will allow rapid dissemination of material lodged entering and leaving each layer that composes them.

The invention will be illustrated in greater detail. referring to the following examples, which should not understood as limiting in the scope of the present invention. In Example 1 the process parameters are chosen in such a way that conventional black carbon is formed in the first (and only) cycle of hydrocarbons through the reactor. By varying the speed of introduction of the power reserve, the enthalpy of gas from the plasma and residence time is seen in Example 2 which in the second cycle that crosses the reactor can produce the Graphite materials with microdomains from PAHs formed in the first cycle.

Example 1

The heavy fuel was heated to 160 ° C and was introduced into the reactor for use in the aligned axial injector of own invention with an introduction speed of 67 kg per hour. The reactor pressure was maintained at 2 bar. As gas from hydrogen hydrogen was used and the rate of introduction of plasma gas was 350 Nm3 / h, while the supply Gross energy from the plasma generator was 620 kW. With this achieved a plasma gas enthalpy of 1.8 kWh / Nm 3 of H 2. The elapsed time since it introduced the atomized oil until the product left the reactor was approximately 0.23 seconds.

The resulting carbon black was the amorphous Traditional quality N-7xx. Volatile content measured on carbon black was 0.6%.

Example 2

In this example, the introduction speed of the oil, enthalpy of plasma hydrogen gas and the time of stay adjusted in a direction such that hydrocarbons evaporated did not reach the pyrolysis temperature during first cycle. The time of stay of the hydrocarbons during the first cycle through the reactors was minimized increasing the rate of introduction of oil and gas from plasma.

The heavy fuel was heated to 160 ° C and was introduced into the reactor for use in the aligned axial injector of its own invention with an introduction speed of 115 kg per hour. The reactor pressure was maintained at 2 bar. The speed of Introduction of plasma hydrogen gas was 450 Nm3 / h, if well the gross power source of the plasma generator was from 1005 kW With this, an enthalpy of plasma gas from 2.2 kWh / Nm 3 of H 2. The elapsed time since it introduced the oil until the PAH left the reactor was approximately 0.16 seconds.

The resulting PAHs were reintroduced into the reactor in the area of the plasma arc to produce a material of Graphite with microdomains, with a yield greater than 90%. He Volatile content measured in the carbon material was 0.7%. All other process parameters were the same as in the first cycle.

Although in the example of the method have been described as a conversion of heavy fuel into graphite materials with microdomains, it should be understood that the method can be apply to all hydrocarbons, both liquid and gaseous. In addition, the method can be performed as a batch or as production continuous, with one or more serial plasma reactors, etc. At case of PAHs formed at the first decomposition stop the materials of the same are reintroduced into the same plasma reactor graphite with microdomains formed in the second step of decomposition will obviously be separated from PAHs by Any suitable conventional method. This method may consist in filtering, cyclone separator, etc.

In addition, it can be used as a plasma gas any gas that is inert and does not contaminate graphite with microdomain products, but hydrogen is especially suitable because this element is in the reserve of feeding. Plasma gas can be recycled back to the inside the reactor, if desired. It is also possible to use the present method by introducing more hydrocarbons through entries on the sides of the decomposition reactor for control the temperature in the zone of decomposition and / or increase yield, see Norwegian patent application no. 176522

References

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5. R. Vincent , N. Burton , PM Lister and JD Wright , Inst. Phys, Conf. Ser ., 138, p. 83, 1993 .

6. Hydrogen & Fuel Cell Letter, vol. 7, no. 2, feb. 1997

7. RM Baum , Chem. Eng. News , 22, p. 8, 1993 .

8. Japanese patent JP 27801 A2, Fullerene-based hydrogen storage media, August 18 1994

9. A. Hirsch , Chemistry of Fullerenes, Thieme Ferlag, Stuttgart, Ch. 5, p. 117, 1994 .

10. BP Tarasov , VN Fokin , AP Moravsky , YM Shul'ga , VA Yartys , Journal of Alloys and Compounds 153-154, p. 25, 1997 .

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12. M. Endo and HW Kroto , J. Phys. Chem . 96, p. 6941, 1992 .

Claims (10)

1. Method for the production of materials graphite with microdomains by decomposing a hydrocarbon fuel in a plasma reactor consisting of a decomposition chamber connected to a plasma generator, in which the plasma reactor is fed with H2 as gas plasma former, characterized in that the hydrocarbon fuel decomposes in a two-step process in which the hydrocarbons are subject to a first decomposition step in which the hydrocarbon fuel is introduced into the decomposition chamber in the vicinity of the arc zone of plasma and is mixed with the plasma gas, and in which the process parameters are adjusted in such a way that the hydrocarbons do not reach the pyrolysis temperature and only partially decompose to form polycyclic aromatic hydrocarbons (PAH), and in the which hydrocarbons in the form of PAH, after the first composition step, are mixed with the plasma gas and reintroduced as part of the plasma gas in the area of the plasma arc in the decomposition chamber and subjected to a second step of decomposition, in which the process parameters are adjusted in such a way that in the area of the plasma arc the PAHs are completely converted in graphite materials with microdomains. 2. Method according to claim 1, characterized in that the reaction chamber connected to a plasma generator is composed of a decomposition chamber constructed as an isolated chamber defined with an outlet for the final products that is connected to a plasma torch in the other extreme 3. Method according to claim 1, characterized in that the graphite materials with microdomains consist of at least one of the materials chosen from the group consisting of carbon nanotubes, fullerenes, carbon microcones and flat carbon sheets with graphite. Method according to claim 3, characterized in that the size of the domains is less than 5 µm in diameter or has a length parallel to the direction of stacking of the graphite and having a thickness less than 100 nm in the direction of stacking of the graphite . 5. Method according to claim 1, characterized in that the conversion rate of hydrocarbons into graphite materials with microdomains is between 0 to 90%. Method according to claim 1, characterized in that the conversion rate of hydrocarbons in graphite materials with microdomains is greater than 90%. Method according to claim 1, characterized in that the conversion rate of hydrocarbons into graphite materials with microdomains is of an industrial order, which is greater than 50 kg / hour, preferably greater than 100 kg / hour and more preferably even higher at 150 kg / hour. Method according to any one of claims 1 to 7, characterized in that at least 10% of the graphite materials with microdomains produced consist of open carbon microconds with a total discrimination greater than 60 °. 9. Method according to any of claims 1 to 8, characterized in that the method uses heavy fuel as an introduced hydrocarbon for conversion into graphite materials with microdomains. 10. Carbon material consisting of graphite materials with microdomains, characterized in that it contains open carbon microconos with total disclinations of 60º and / or 120º, corresponding to cone angles of 112.9º and / or 83.6º, respectively.